1. Field of the Invention
This invention relates to a printer system constituted by a printer controller and a printer interconnected by a bus. The printer controller constituting the printer system supplies the printer with image data via the bus, and the printer prints the image, which is represented by the image data supplied by the printer controller, at a constant speed. The present invention further relates to the printer and printer controller that construct this printer system. The present invention relates to a method of controlling the operation of the printer system, a method of controlling the operation of the printer and a method of controlling the operation of the printer controller.
2. Description of the Background Art
Parallel communication using a Centronics interface or an SCSI (Small Computer System Interface) and serial communication using an RS232C, RS422 or USB (Universal Serial Bus) are utilized to transmit image data from a printer controller to a printer. With these communication schemes, image data is transmitted from the printer controller to the printer irrespective of the printing speed of the printer. It is required that the printer be provided with an image memory having enough storage capacity to store image data representing at least one frame of an image (the image printed on one sheet of paper). This makes it difficult to lower the cost of the printer.
Accordingly, an object of the present invention is to make it possible to construct a printer using an image memory having a comparatively small storage capacity.
In order to supply a printer with image data from a printer controller, the present invention utilizes IEEE (Institute of Electrical and Electronic Engineers, Inc.) Standard 1394 for high-speed serial transmission. With IEEE Standard 1394, which is currently under consideration in the art, isochronous transfer and asynchronous transfer are possible.
With isochronous transfer, data referred to as cycle-start packet data is in principle generated at an isochronous cycle (125 xcexcs) by any of a plurality of nodes connected by a bus. Data is transmitted from a certain node (this node is a cycle master, as will be described later) to another node every isochronous cycle. Isochronous transfer, which makes it possible to perform data transmission without fail within the isochronous cycle, transmits data unilaterally from the transmitter to the receiver. Asynchronous transfer is such that when the receiver receives transmitted data, a signal indicating that the data has been received is sent back to the transmitter.
A first aspect of the present invention provides a printer system constituted by a printer and a printer controller. The printer and the printer controller in this printer system are connected by a bus, and the printer controller supplies the printer with image data via the bus. The printer prints the image, which is represented by image data supplied by the printer controller, at a constant speed.
The printer is equipped with a buffer memory having an image-data storage capacity smaller than the quantity of image data representing one frame of the image, the buffer memory temporarily storing the image data supplied by the printer controller. Either the printer or the printer controller is provided with a device for generating a start signal which indicates start of supply of the image data.
The printer controller has image-data transmission start control means (an image-data transmission start controller) for starting transmission of image data to the printer in packet units upon elapse of a predetermined period of time from generation of the start signal, and image-data transmission control means (an image-data transmission controller) for repeating, in packet units, the transmission of image data to the printer in such a manner that the image data that has been stored in the buffer memory will not be emptied from the buffer memory.
The printer has storage control means (a storage controller) for receiving image data transmitted from the printer controller and storing this image data in the buffer memory, and printing control means (a printing controller) for reading out the image data that has been stored in the buffer memory and printing an image, which is represented by the image data read out, at a constant speed.
The first aspect of the present invention also provides an operation control method suited to the printer system described above. Specifically, there is provided a method of controlling operation of a printer system constituted by a printer controller and a printer connected by a bus, wherein the printer controller supplies the printer with image data via the bus and an image, which is represented by image data supplied by the printer controller, is printed in the printer at a constant speed. The printer is provided with a buffer memory having an image-data storage capacity smaller than the quantity of image data representing one frame of the image, the buffer memory temporarily storing the image data supplied, and either the printer or the printer controller generates a start signal.
The method further includes starting transmission of image data from the printer controller upon elapse of a predetermined period of time from generation of the start signal, repeating, in packet units, the transmission of image data from the printer controller in such a manner that the image data that has been stored in the buffer memory will not be emptied from the buffer memory, and, in the printer, receiving image data transmitted from the printer controller, storing this image data in the buffer memory, reading out image data that has been stored in the buffer memory and printing an image, which is represented by the image data read out, at a constant speed.
In accordance with the first aspect of the present invention, the printer is provided with the buffer memory having a storage capacity capable of storing image data the amount of which is less than the amount of image data representing one frame of an image (which means, as described above, the image printed on one sheet of paper).
In the printer controller, transmission of image data to the printer from the printer controller in packet units is started upon elapse of a predetermined period of time from generation of the start signal, and transmission of the image data to the printer from the printer controller in packet units is repeated in such a manner that the image data that has been stored in the buffer memory will not be emptied from the buffer memory.
The image data that has been transmitted is received by the printer in packet units and is stored temporarily in the buffer memory of the printer. The image data that has been stored in the buffer memory is read out and the image represented by the read image data is printed at a constant speed.
The printer need not be provided with a memory having a large storage capacity capable of storing the quantity of image data representing one frame of an image. It will suffice to provide the printer with a buffer memory of small capacity, thereby lowering the cost of the printer.
The continuity of image data can be maintained because succeeding data is transmitted from the printer controller before the data already in the buffer memory vanishes. Accordingly, the printer used can be one which prints images at a constant speed.
Printing speed data representing the printing speed and storage capacity data representing the storage capacity of the buffer memory may be stored in the printer. In such case the stored printing speed data and storage capacity data would be transmitted to the printer controller.
The printer controller receives the printing speed data and storage capacity data transmitted from the printer and determines the amount of image data included in a packet based upon the printing speed data and storage capacity data received.
The printing speed and the storage capacity of the buffer memory may be entered into the printer controller. In such case the amount of data included in a packet would be determined based upon the printing speed data and storage capacity data entered.
In either case, the optimum amount of image data included in a packet can be determined.
A print preparation command may be transmitted from the printer controller to the printer before the start of the printing operation by the printer. In such case printing preparation inclusive of positioning printing paper at a home position would be performed in response to the printing preparation command transmitted from the printer controller, printing preparation-end data representing end of printing preparation would be transmitted to the printer controller in response to end of printing preparation, and the above-mentioned start signal would be generated following the transmission of the printing preparation-end data.
Since the image data is transmitted from the printer controller to the printer upon completion of printing preparations, the image data can be prevented from being transmitted before the printer has attained a state in which it is capable of printing. This precludes printing processing errors.
Command identification data may be added to the printing preparation command to indicate that it is a command, and image-data identification data may be added to the image data transmitted from the printer controller to indicate that this data is image data. In this case, whether received data is the printing preparation command or the image data is judged in the printer based upon the command identification data or image-data identification data, the printer performs printing preparation in response to judging that the received data is the printing preparation command and prints the image represented by the image data in response to judging that the received data is the image data.
Since received data can thus be recognized immediately as being a command or image data, printing preparation and printing can be executed rapidly.
An arrangement may be adopted in which the printer controller is equipped with first and second control means (a first controller and a second controller), wherein the first controller is made to perform transmission control relating to transmission of image data to the printer, and the second controller is made to control operations other than transmission control.
As a result, the burden of the control operation by the second controller is alleviated.
There may be a plurality of the printers, each may be assigned a specific printer identification symbol (channel number or ID), and printer identification data which represents the specific printer identification symbol may be added to the image data output by the printer controller.
In this case it is determined in the printer whether the printer identification symbol represented by the printer identification data added onto the received image data agrees with the assigned printer identification symbol. If it is judged that the two agree, the printer performs printing by a printing head based upon the image data having the attached printer identification data representing the identification symbol of the printer.
Desired image data can be transmitted only to a desired printer even in a case where a plurality of printers have been connected to the printer controller. The same image data can be transmitted to all of the printers as a matter of course.
A second aspect of the present invention provides a printer system constituted by a printer and a printer controller. The printer and the printer controller in this printer system are connected by a bus, and the printer controller supplies the printer with image data via the bus. The printer prints the image, which is represented by image data supplied by the printer controller, at a constant speed.
The printer is equipped with a buffer memory having an image-data storage capacity smaller than the quantity of image data representing one frame of the image, the buffer memory temporarily storing the image data supplied by the printer controller, and with means for outputting an image-data transfer request.
The printer controller has image-data transmission control means for transmitting image data to the printer in packet units in response to output of the transfer request.
The printer has storage control means for receiving image data transmitted from the printer controller and storing this image data in the buffer memory, and printing control means for reading out the image data that has been stored in the buffer memory and printing an image, which is represented by the image data read out, at a constant speed.
The second aspect of the present invention also provides an operation control method suited to the printer system described above. Specifically, there is provided a method of controlling operation of a printer system constituted by a printer controller and a printer connected by a bus, wherein the printer controller supplies the printer with image data via the bus and an image, which is represented by image data supplied by the printer controller, is printed in the printer at a constant speed. The printer is provided with a buffer memory having an image-data storage capacity smaller than the quantity of image data representing one frame of the image, the buffer memory temporarily storing the image data supplied by the printer controller, and means for outputting an image-data transfer request.
The method further includes transmitting image data from the printer controller in packet units in response to output of the transfer request from the printer, and, in the printer, receiving image data transmitted from the printer controller, storing this image data in the buffer memory, reading out image data that has been stored in the buffer memory and printing an image, which is represented by the image data read out, at a constant speed.
In the second aspect of the present invention as well, the printer need not be provided with a memory having a large storage capacity capable of storing the quantity of image data representing one frame of an image. It will suffice to provide the printer with a buffer memory of small capacity, thereby lowering the cost of the printer.
It will suffice if the transfer request is output from the printer substantially whenever one line of one frame of an image is printed, by way of example.
Further, the continuity of the image data can be maintained by having the printer output the image-data transfer request in such a manner that the image data that has been stored in the buffer memory will not vanish from the buffer memory.
Furthermore, the amount of image data included in the packet may be changed and the image data transmitted from the controller in such a manner that the image data that has been stored in the buffer memory will not vanish.
It may be so arranged that after image data has been transmitted by the image-data transmission controller in response to output of the transfer request, the transmission of null data is repeated by the printer controller in packet units until the next output of the transfer request.
Thus, the amount of image data that is stored in the buffer memory can be adjusted.
The printer preferably performs printing-related preparations (printer heat-up, positioning of the printing paper, positioning of the printing head, etc.) in response to entry of a printing-preparation setting request command. In such case the above-mentioned transfer request would be output upon completion of the printing-related preparations. Image data can be prevented from being transferred from the printer controller before the printing-related preparations are completed.
The printing-preparation setting request command may be output from the printer controller. In this case the printer controller repeats the transmission of null data in packet units from output of the printing-preparation setting request command to output of the transfer request.
A predetermined routine can be used without changing the routine for transmitting the image data.
In a case where a plurality of printers have been connected to the printer controller, the printer controller would respond to output of the transfer request from all printers by transmitting image data to all of these printers in packet units.
In both the first and second aspects of the present invention, the printer and printer controller constituting the printer system can be arranged so as to be separate from each other.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.